1. Field of the Invention
This invention relates to the field of integrated circuits. More particularly, this invention relates to the testing of integrated circuits to ensure there correct operation.
2. Description of the Prior Art
It is known to provide integrated circuit with mechanisms to permit test operations to be performed on the integrated circuits to ensure their correct operation. These tests may be performed after manufacture to ensure the integrated circuits are properly formed and function correctly before they are used. One known type of testing mechanism uses serial scan chains embedded within the integrated circuit to apply stimulus signals to nodes within the integrated circuit and then to capture response signals from the integrated circuit. The observed response signals are then compared with expected response signals. Any difference between the observed response signals and the expected response signals indicate that the integrated circuit is not formed or operating correctly.
While such manufacturing tests performed using serial scan chain are effective at identifying manufacturing defects, there exist the possibility that an integrated circuit may ceased the function when it is incorporated within a larger device or during its later use within that larger device, e.g. due to wear out, particle strike damage etc. This problem is particularly significant when the integrated circuit is involved within a safety critical system, such as the braking system of a car. Such safety critical applications often require the integrated circuit to rapidly respond to detected conditions and this capability should not be interrupted when the integrated circuit is in use.